Abrasive blasting devices operate on the physical property that gas at a higher pressure flows towards and into gas at lower pressure. When abrasive powder is mixed with gas at higher pressure, the gas carries the abrasive powder as the gas accelerates and flows to the lower pressure. As the gas and abrasive powder blast the target material at high speed, the impact of the particles removes layers of the target material. In dentistry this technology is known as micro-abrasion and is used to achieve a variety of goals—such as to remove foreign material or to dull a shiny surface, roughen or etch the surface to enhance bonding quality and to remove decay by drilling and cutting tooth structure.
Air abrasion devices are disclosed in U.S. Pat. No. 2,612,732 (Ziegler), U.S. Pat. No. 2,725,684 (Crow), U.S. Pat. No. 3,626,841 (Schachter) and U.S. Pat. No. 2,441,441 (Paache), and fall into two main categories: (i) providing a separate mixing apparatus for generating the abrasive laden air stream and delivering the abrasive laden air stream through an extended hand-piece for directing the stream onto the target surface, and (ii) integrating the mixing apparatus into the hand-held device.
The first category of devices facilitate more complex mechanisms and many operational options since the size and weight of the device are of no concern. Because the extended hand-piece delivers the abrasive laden air stream independent of the mixing operation, the hand-piece can be held at any orientation during operation. U.S. Pat. No. 6,083,001 (Deardon et al.) discloses a dental air abrasion system in which the flow of the particles is electronically controlled by pressure differentials. U.S. Pat. No. 6,093,021 (Rainey) discloses an automated control system which utilizes a gas stream mounted particulate sensor to regulate fluid flow rates into and around the ultrasonically agitated mixing chamber in order to accurately maintain the abrasive concentration in the air stream. Various methods for reducing the overspray of the abrasive have also been developed for these devices. U.S. Pat. No. 5,356,292 (Ho), U.S. Pat. No. 5,197,876 (Coston), and U.S. Pat. No. 6,024,566 (Burns et al.) disclose add-on splatter guard and collector attachments to air abrasion devices.
In the second category, the size, weight, and ergonomic shape of the device are significant factors. U.S. Pat. No. 5,199,299 (Herald et al.) and U.S. Pat. No. 6,439,966 (Burns et al.) disclose innovative hand-holdable air abrasion devices which mount the mixing apparatus into the hand-piece. The drawback of this approach is that the operation of these devices is limited by the orientation of the mixing chamber. An adjunct to the second category of devices has been the concept of simple self-contained air abrasion devices—such as U.S. Pat. No. 5,839,946 (Hertz), U.S. Pat. No. 6,287,180 (Hertz), U.S. Pat. No. 6,951,505 (Hertz), and U.S. Pat. No. 7,226,342 (Hertz), U.S. Pat. No. 6,398,628 (Groman), U.S. Pat. No. 6,347,984 (Groman), Schur et al. U.S. Pat. No. 6,004,191, and U.S. Pat. No. 6,354,924 (Trafton et al.). These devices rely on the air stream to perturb the abrasive and generate the mixing action based on U.S. Pat. No. 4,475,370 (Stark et al.) fixed air abrasion device for treating dental castings.
Merging of Stark's blow-through mixing method into the hand-piece so the mixing chamber is held between the user's fingers has taken air abrasion art to a new level. Because of their simplified structures, simple self-contained air abrasion devices tend to be less expensive to manufacture and can therefore be marketed to the user as disposable instruments.
With increased emphasis in Medical, Pharmaceutical, Cosmetic and Dental applications on reduced cross-patient contamination, there has been a significant drive towards single usage disposable packaging and devices. With advances in materials and fabrication technologies the cost of these devices has been significantly reduced. U.S. Pat. No. 4,391,590 (Dougherty) discloses a syringe and stopper like cartridge device for dispensing material while U.S. Pat. No. 5,839,946 (Hertz) discloses the formulation an air abrasion instrument from a syringe and stopper type structure. Both innovations capitalize on the lower cost of fabrication and the well established production methods of a syringe and stopper configuration.
Simple self-contained prior art air abrasion devices support an elongated cylindrical chamber with an inlet conduit for delivering the air into the mixing chamber and a discharge conduit for carrying the air-abrasive mixture out of the mixing chamber. The mixing chambers are utilized as a reservoir for storing the abrasive powder. Once the reservoir is depleted of abrasive material, the devices are discarded and therefore function as disposable instruments which do not require sterilization post intra-oral use.
To prevent the abrasive material from escaping the mixing chamber or becoming contaminated prior to use, simple self-contained prior art air abrasion devices add additional components which seal the inlet and outlet ports and conduits. While the U.S. Pat. No. 5,839,946 (Hertz), and U.S. Pat. No. 6,004,191 (Schur et al.) devices include passive caps which must be removed prior to using the instrument, U.S. Pat. No. 6,951,505 (Hertz) and U.S. Pat. No. 6,287,180 (Hertz), and U.S. Pat. No. 6,398,628 (Groman) and U.S. Pat. No. 6,347,984 (Groman) add functional components which actively prevent the abrasive from exiting the mixing chamber. U.S. Pat. No. 6,398,628 (Groman) discloses a filter that prevents the abrasive from exiting the device's inlet port and a movable discharge conduit which prevents abrasive material from exiting the mixing chamber when the discharge conduit inlet port abuts the side wall of the mixing chamber. U.S. Pat. No. 6,951,505 (Hertz) has a deformable seal at the inlet port external to the mixing chamber which functions as a check-valve that allows the pressurized-gas to enter the instrument but prevents abrasive from exiting the instrument. U.S. Pat. No. 6,398,628 (Groman) discloses a deformable and movable cap configurations which block both the delivery conduit inlet and discharge conduit outlet prior to use.
Another disposable delivery method disclosed by U.S. Pat. No. 6,343,717 (Zhang et al.) attempts to address the containment of stored material utilizing a pipette structure. A typical pipette consists of a slender pipe or tube that is used to transfer or measure small quantities of material from one location to another. The most common type of pipette consists of a small tube that widens into a bulb at the middle. The Zhang et al. pipette structure is made of a rigid or resilient material that is pre-filled with a pharmaceutical or cosmetic product and is used once and then discarded. Zhang et al. discloses a plurality of ways by which the disposable pipette can be sealed to contain the material and then unsealed by the user prior to use for dispensing the stored material. According to Zhang's et al. invention the majority of material is retained within the bulb section of the pipette, but Zhang's et al. sealing methods permit the contained material to migrate into the top and bottom tube sections. Although Zhang's et al. use of a pipette structure leads to a very cost effective means of delivering the contained material, Zhang's et al. sealing methods are not compatible with the needs of air abrasion devices.
Pressurized air stream is delivered to the simple self-contained air abrasion devices of Hertz, Groman, Schur, and Trafton via custom connectors which engage the device externally and to form a seal with the device body to deliver the pressurized air to the mixing chamber delivery port. The connectors are designed to supply clean dry air in order to maintain the abrasive powder dry, since any moisture causes clumping of the abrasive material and therefore the malfunction of the device. The dry air is required because the gas delivery conduit leads directly into the mixing chamber; therefore any liquid present at the entry to the device gets trapped in the mixing chamber. U.S. Pat. No. 6,293,856 (Hertz et al.) discloses a connector with additional conduits for carrying other types of fluids passively through the mixing chamber. This configuration requires a very complex connector to assure the separation of the fluids delivered to the air abrasion instrument without contaminating the mixing chamber. Custom connectors which supply dry air add to the installation cost and complexity of these disposable devices. And because they attach to the body of the devices, these connectors are typically very bulky.
Referring to FIGS. 1A, 1B, prior art self-contained air abrasion devices use a blow-through methodology to agitate the abrasive powder. More specifically, these devices utilize the delivery conduit to deliver the gas stream into the abrasive material. As the gas stream blows through the abrasive material, the abrasive material is agitated. Gravity is utilized to assure that the non-aerated abrasive remains at the bottom of the mixing chamber. As the air stream reverses direction towards the discharge conduit inlet, aerated particles are captured by the air stream. The abrasive laden air stream is pushed out of the mixing chamber through the discharge conduit by the higher pressure gas source.
In their reduction to practice, both the Schur and Groman devices require the user to maintain the orientation of the device so the mixing chamber points downward. The attached user instructions for the Schur and Groman devices outline the specific user instructions cautioning the user about mis-orienting the mixing chamber. To compensate for his shortcoming, the marketed Groman instrument provides a finger bendable discharge conduit. The marketed Schur device provides a bending tool, so the user is able to form the delivery conduit to reach upper surfaces while maintaining the proper orientation of the mixing chamber.
Referring to FIG. 2, if the user attempts to utilize these prior art devices with the mixing chamber horizontal or upside down, the abrasive material is pushed directly into the discharge conduit without being properly mixed with the air steam. This leads to a concentration of abrasive material to exit the device in an uncontrolled manner, which creates a cloud of abrasive dust or clogs up the discharge conduit as the abrasive powder binds. Additionally, in certain orientations the delivery conduit is not immersed in the abrasive material which also disrupts the mixing operation of these prior art devices. In fact, the pressurized-gas exiting the delivery conduit creates a back pressure on the abrasive within the mixing chamber causing the abrasive powder particles to bind together instead of mix with the air stream. Most importantly, these disruption in flow can lead to a defective clinical procedure which either under or over etches the target tooth surface.